Garage door openers are known for moving overhead garage doors between open and shut positions, usually in response to a radio signal from a car transmitter or in response to an electrical signal generated by an electrical switch. While such openers have received widespread commercial acceptance, there are still several problems which have not been fully overcome. One of such problems is the ability to quickly and easily adapt the door opener for manual operation so that the door can be lowered or raised during a power failure. Another of such problems is providing reliable and accurate means for controlling the movement of the door between fully open and fully closed positions.
The problems of alternately coupling and uncoupling a garage door to an electrically powered drive system is complicated by the fact that in most garage door openers a drive linkage must be securely coupled to the door. Most drive systems include some sort of track with a gear rod mounted within the track and a carrier engaging the gears for movement along the track. The carrier, in turn, is coupled to the door. A typical garage door opener is shown in Houk's U.S. Pat. No. 3,051,014 issued Aug. 28, 1962, for "Screw and Nut Mechanism" and this patent discusses the problem of manual versus power operation and one mechanism for disconnecting a carrier from the drive gear.
The disconnect system of the Houk Patent includes a cam device which is rotatable into a first position for urging a nut into contact with a drive screw and which is rotatable into a second position to locate the nut away from the drive screw and permit manual operation of an overhead garage door. A compression spring is provided for retaining the cam follower control rod in one of its two operating positions. While the system does permit disconnection of the door-opener linkage from the drive gear, it is relatively complex in terms of manufacture and operation and the use of a compression spring as part of the system could lead to failure in the event of spring fatigue.
Several types of devices are incorporated in prior art garage door openers for controlling the movement of the door between open and shut positions. Most typically such devices incorporate limit switches triggered by the door opener linkage or a timing device which activates the drive system for a predetermined time. While most of these systems have satisfactory reliability, there is a tendency for the accuracy to diminish after extended use and some garage constructions make it difficult to easily and properly install the limit devices.
A garage door opener which overcomes the aforementioned disadvantages would be a significant advance in this technology.